10 



RADIATION' laoLOGY 



imim alisorption do not coiiicidc for the two phases. Approximately the 

 same iiumher of al)sorption hands exist at wave lengths helow 1.9 fi, hut 

 the \apor hands app(Mir at somewhat shoi-ter \va\'e lenf^ths than the liquid 

 bands. 



Therefore sunlight that reaches the earth through several centimeters of 

 precipitahle water vapor is not entirely' depleted of energy capable of 

 being absorbed !)>■ liiiuid w atcr in organisms or in the seas, and, in particu- 

 lar, this is true in the so-called "atmospheric windows" at 1.65 and 2.2 n, 



I 17mm WATER VAPOR 



17mm WATER VAPOR 



0.05 



0.04 



0.03 



0.02 



o 



0.01 



7 8 9 



WAVE LENGTH,/^ 



Fig. 3-15. Solar intensity I'o in tho infrared and transmission of water vapor, ozone, and 

 carbon dioxide. 



where atmospheric water vapor transmits copiously and relatively small 

 thicknesses of liquid water absorb strongly. The effect of absorption 

 in the infrared is to heat the absorber. In the 2.2-/i region and at longer 

 wave lengths where liquid water is highly absorbing, heating is produced 

 principally at the surface. On the other hand, for shorter wave lengths 

 below 1 /i, the radiation peiietrates to a greater depth before being com- 

 pletely absorbed and produces warming in depth. 



Figure 3-15 is an extension of the solar-intensity and the atmospheric- 

 transmission curves of Fig. 3-14 to 14 n to show other atmospheric infra- 

 red absorption bands. The absorption at 2.7 m is due to both carbon 

 dioxide and water vapor. The strong absorption at 4.2 fx is due to carbon 

 dioxide, and the great band from 5.2 to 7.5 /x is due to water vapor. 

 Beyond this band to about 14 ^l the lower atmosphere is relatively trans- 



